Preparation of optically-active cyanomethyl esters

ABSTRACT

Optically-active alpha-cyano esters are prepared by treating a non-symmetrical ketene with a racemic or an optically-active alpha-hydroxynitrile or with an aldehyde and cyanide ions in the presence of an optically-active amine catalyst.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Ser. No. 443,513,filed Nov. 22, 1982, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to processes for the preparation ofoptically-active cyanomethyl esters and novel catalysts therefor.

2. Description of the Prior Art

Stereoisomers of cyanomethyl esters of alpha-chiral carboxylic acids orthe acids themselves usually have different effects in biologicalsystems. In the past, it usually had not been simple to prepare suchoptically-active cyanomethyl esters directly because the correspondingchiral alpha-hydroxynitriles were not always readily available. Evenwhen these optically-active alpha-hydroxynitriles were available orbecame more readily available, the optically-active acids were notalways readily accessible. Often, the optically-active acids wereobtained by classical resolution, which was usually time consuming andnot practical on a large scale.

The present process provides a process for preparing optically-activecyanomethyl esters of alpha-chiral carboxylic acids in high yield by adirect synthesis method, avoiding the cumbersome classical resolution ofthe corresponding optically-active acids and alcohols.

SUMMARY OF THE INVENTION

The present invention is directed to a process for the preparation of anoptically-active cyanomethyl ester of an alpha-chiral (optically-active)carboxylic acid (i.e. alpha-chiral cyanomethyl esters of alpha-chiralcarboxylic acids), or a mixture enriched therein, which comprisestreating a non-symmetrical ketene with a racemic or an optically-activealpha-hydroxynitrile in the presence of an optically-active (chiral)tertiary amine catalyst. The optically-active cyanomethyl ester productsinclude those of formula I below ##STR1## wherein R¹, R², R³ and R⁴ aresubstitutents; * denotes the asymmetrically substituted carbon atom, andthe broken lines are optional bonds.

The reaction is conducted in the presence or absence of a solvent. Whena solvent is used the solvent is preferably a non-hydroxylic solventsuch as hydrocarbons, chlorinated hydrocarbons, ethers and the like. Forexample, suitable solvents are alkanes containing from 5 to 10 carbonatoms such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane,n-decane and their isomers. Petroleum fractions rich in alkanes are alsosuitable, for example, gasoline with a boiling range at atmosphericpressure of between 40° and 65° C., between 60° and 80° C. or between80° and 110° C. Petroleum ether is also suitable. Cyclohexane andmethylcyclohexanes are examples of useful cycloalkanes containing from 6to 8 carbon atoms. Aromatic hydrocarbon solvents can contain from 6 to10 carbon atoms, for example, benzene, toluene, o-, m- and p-xylene, thetrimethylbenzenes, p-ethyltoluene and the like. Suitable chlorinatedhydrocarbons contain from 1 to 4 chlorine atoms in combination with analkane chain containing from 1 to 4 carbon atoms or with a benzene ring,for example, carbon tetrachloride, chloroform, dichloromethane,1,2-dichloroethane, trichloroethane, perchloroethane, chlorobenzene and1,2- or 1,3-dichlorobenzene and the like. Ethers are generally thosecontaining from 4 to 6 carbon atoms such as diethyl ether, methyltert-butyl ether and diisopropyl ether and the like. The solvent ispreferably an aromatic solvent, especially toluene.

Any non-symmetrical ketone is useful (provided it does not containsubstituent groups which form other stable reaction products with thealpha-hydroxynitrile. The non-symmetrical ketenes have the formula II##STR2## wherein R¹ and R² each independently is a different alkyl,aralkyl, alkoxy, aryloxy, alkylthio, alkylsulfonyl, arylthio, orarylsulfonyl group containing from 1 to 10 carbon atoms, or a cycloalkylgroup containing 3 to 7 ring carbon atoms, or R² is also an alkenyl oralkynyl group containing 2 to 10 carbon atoms; a naphthyl group; aphenyl group; a heterocyclic group containing 5 or 6 ring atoms, one ofwhich is oxygen, sulfur or nitrogen, and the remainder are carbon atoms;or an amino group disubstituted by acyl or alkyl containing up to 10carbon atoms or a phenyl group; or R¹ and R², when taken together withthe carbon atom to which they are attached, form a non-symmetricalcycloalkyl group containing 4 to 7 ring carbon atoms and 4 to 14 carbonatoms. The R¹ and R² groups can be optionally substituted by one or moreof halogen atoms having an atomic number of from 9 to 35, alkyl orhaloalkyl containing 1 to 4 carbon atoms, alkenyl or haloalkenylcontaining 2 to 4 carbon atoms, haloalkoxy or alkoxy of 1 to 4 carbonatoms, haloalkylthio or alkylthio of 1 to 4 carbon atoms or equivalentkinds and sizes of substituents which may contain the same or greatercarbon number.

One embodiment of non-symmetrical ketenes used in the process of theinvention is that which results in pyrethroid esters, including thoseesters having an acid moiety described in U.S. Pat. Nos. 4,062,968 and4,199,595. Examples of such ketenes include those having the formula IIin which R¹ is isopropyl or cyclopropyl optionally substituted by one ormore chlorine atoms; R² is an alkyl group containing 1 to 6 carbonatoms; an alkenyl group containing 2 to 6 carbon atoms; a naphthylgroup; a phenyl group or a (benzyloxycarbonyl)phenylamino group, eachoptionally ring-substituted by one or more of halogen, alkyl, haloalkyl,alkoxy or haloalkoxy in which the halogens are bromine, chlorine orfluorine, and the alkyl groups contain 1 to 4 carbon atoms.

Of particular interest as non-symmetrical ketene reactants because theirresulting esters are usually highly pesticidally active are thoseketenes having the formula II in which R¹ is isopropyl; R² is a phenylgroup para-substituted by halogen, alkyl, haloalkoxy in which thehalogen is, e.g. chlorine or fluorine, and the alkyl contains 1 to 4carbon atoms, e.g. methyl.

For example, the non-symmetrical ketene is(4-chlorophenyl)isopropylketene,(4-(difluoromethoxy)phenyl)isopropylketene,(4-trifluoromethyl)-3-chlorophenyl)(benzyloxycarbonyl)amino)isopropylketene,and the like.

Any racemic or optically-active alpha-hydroxynitrile is useful (providedit does not contain substituent groups which form other stable reactionproducts with the non-symmetrical ketene or the catalyst). Preferably,the alpha-hydroxynitrile is a symmetrical or non-symmetrical, racemic oroptically-active alpha-hydroxynitrile of formula III ##STR3## wherein R³is an optionally-substituted hydrocarbyl or heterocyclic group; and R⁴is an optionally substituted hydrocarbyl group or a hydrogen atom or R³and R⁴ together with the carbon atom to which they are attached form acarbocyclic group as denoted by the dotted line.

The hydrocarbyl groups represented by R³ and R⁴ in the formula III maybe, for example, an alkyl, a cycloalkyl or an aryl group of up to 20carbon atoms, preferably up to 10 carbon atoms, or R³ in the formula IIImay be a carbocyclic or an O or S heterocyclic aryl group. Examples ofcarbocyclic aryl groups are phenyl, 1-naphthyl, 2-naphthyl and 2-anthrylgroups. Heterocyclic aromatic groups are derived from hetero-aromaticcompounds which are defined as in Kirk-Othmer, "Encyclopedia of ChemicalTechnology", Second Edition, Volume 2 (1963), page 702: obtained byreplacement of one or more carbon atoms of a carbocyclic aromaticcompound by a heteroatom selected from O or S--and also include thoseheterocyclic compounds having five-membered rings which show aromaticcharacteristics and are mentioned on page 703 of said volume. Optionalsubstituents include one or more of halogen atoms having an atomicnumber of from 9 to 35, inclusive, or an alkyl, alkenyl or alkoxy groupcontaining 1 to 6 carbon atoms, each optionally substituted by one ormore halogen atoms, optionally substituted phenoxy, phenyl, benzyl orbenzoyl and equivalent kinds of substituents. Illustrative examples ofthe optically-active alpha-hydroxynitriles includealpha-hydroxy-alpha-methylbutyronitrile,alpha-hydroxy-alpha-methylbenzeneacetonitrile,alpha-hydroxyisobutyronitrile and the like.

Preferably, the alpha-hydroxynitrile compound has the formula ##STR4##wherein each A is independently a hydrogen atom, a halogen atom havingan atomic number of from 9 to 35, inclusive, or an alkyl, alkenyl oralkoxy group containing 1 to 6 carbon atoms, each optionally substitutedby one or more halogen atoms having an atomic number of from 9 to 35,inclusive; B is a hydrogen atom, a halogen atom having an atomic numberof from 9 to 35, inclusive, or an alkyl, alkenyl or alkoxy groupcontaining 1 to 6 carbon atoms, each optionally substituted by one ormore halogen atoms having an atomic number of from 9 to 35, inclusive,or is a group ##STR5## in which Y is O, CH₂, or C(O); m is 0 or 1 and Dand E each independently is a hydrogen atom, a halogen atom having anatomic number of from 9 to 35, inclusive, or an alkyl, alkenyl or alkoxygroup containing 1 to 6 carbon atoms, each optionally substituted by oneor more halogen atoms having an atomic number of from 9 to 35,inclusive.

Preferably, the (optically-active) alpha-hydroxynitrile can have the R-or S-configuration, and therefore, include either the R- or, preferablyS-alpha-hydroxynitrile of the formula ##STR6## wherein Y is O, CH₂, orC(O); each A, D and E independently is a hydrogen atom, a halogen atomhaving an atomic number of from 9 to 35, inclusive, or an alkyl, alkenylor alkoxy group containing 1 to 6 carbon atoms, each optionallysubstituted by one or more halogen atoms having an atomic number of from9 to 35, inclusive. Preferably, each A, D or E independently is ahydrogen atom, a fluorine atom, a chlorine atom, a methyl group, atrifluoromethyl group or a methoxy group. Preferably, one of D and E isa hydrogen atom. An especially preferred subclass ofS-alpha-hydroxynitriles are those of the formula above in which D is ahydrogen atom and A and E each independently is a fluorine atom or ahydrogen atom, and, preferably, when either A or E is fluorine, each islocated at the 4-position of the ring relative to the benzyl carbon whenA or relative to the Y═O bearing carbon atom when E. Especially suitablealcohols are when A is a fluorine atom at the 4-position or a hydrogenatom and E is a hydrogen atom.

Examples of alpha-hydroxynitriles of the above formula includeS-alpha-cyano-3-phenoxybenzyl alcohol,S-alpha-cyano-4-fluoro-3-phenoxybenzyl alcohol,S-alpha-cyano-3-(4-fluorophenoxy)benzyl alcohol, and their correspondingenantiomers.

The optically-active (chiral) tertiary amine catalyst is anyoptionally-substituted alkyl, cycloalkyl, aromatic or heterocyclic mono-or polyamine containing up to 40 carbon atoms (including polymers andcopolymers and amine salts and the like), which will not interfere withthe reaction. The amine is preferably a moderate to weakly basic amine.The optically-active amines, polymers and copolymers are conventionalkinds of materials known in the art and can be prepared by known methodsexcept for certain novel ketene reaction products discussed below. Forexample, numerous optically-active amines are specifically disclosed inNewman, P., "Optical Resolution Procedures for Chemical Compounds", Vol.1, Amines and Related Compounds, Optical Resolution Information Center,Manhattan College, Riverdale, N.Y., Library of Congress Catalog Card No.78-61452. This reference also discloses optically-active mono-, di- andpolyamines which can be polymerized and co-polymerized by knownprocedures to form optically-active polymeric amines for use in theinvention.

One embodiment of the optically-active tertiaryamine catalyst comprisesa substituted optically-active amino acid which is preferably anyacyclic, carbocyclic, aromatic or heterocyclic amino acid containing upto 20 carbon atoms, preferably up to 10 carbon atoms, additionallysubstituted by a moderate to weakly basic nitrogen base substituent oris the reaction product thereof with about one to about three moles of aketene. Suitable nitrogen-base substituents include optionallysubstituted nitrogen-heterocyclic groups or amino groups, eachoptionally substituted by alkyl or cycloalkyl groups containing 1 to 6carbon atoms or by optionally substituted phenyls. Other optionalsubstituents include hydroxy, alkyl, alkoxy, amino, alkylthio,phosphoryloxy, amido and the like. Examples of nitrogen-heterocyclicgroups include thiazolyl, imidazolyl, pyrrolyl, benzopyrrolyl and thelike.

Non-limiting examples of the optically-active catalyst includebeta-aminoalanine, ornithine, canavanine, anserine, kynurenin, mimosine,cystathionine, ephedrin, acylated ephedrins, histidinol, citrulline,carbamoylserine, cinchonine, quinine or acylated quinuclidinyl alcohols.

Another embodiment of the amine catalysts are the heterocyclic aminesand polymers of heterocyclic amines. Non-limiting examples include di-and polyaziridines, polymers of acryloylcinchonines alone or withN,N-diacryloylhexamethylenediamine, di- and poly(iminoisobutylethylene),polymers of (N-benzyl-2-pyrrolidinylmethyl ester) with acrylate or alower alkanoic acid, and like materials.

In another embodiment of the invention, the catalyst is anoptically-active histidine-containing peptide; or is ahistidine-containing di- or polypeptide; in which at least one of thehistidinyl free N--H and free COOH groups is optionally modified with aprotecting group into the form of an amide (or acid addition saltthereof) and an ester group, respectively; or the reaction product ofone mole of a histidine or a histidine-containing di- or polypeptidewith from about one mole to three moles of a ketene per mole ofhistidine group.

The di- or polypeptide is linear or cyclic. These peptides usuallycontain from about 2 up to about 16 peptide units, preferably 2 to 4peptide units. Nitrogen-substituted amino acids, including thesehistidine-containing di- and polypeptides, are prepared by conventionalpeptide synthesis, for example, as in Greenstein, J. P. and M. Winitz,"Chemistry of the Amino Acids", John Wiley & Sons, Inc., New York, 1961.

The dipeptides of the histidine-containing catalyst are preferred,especially in the cyclic dipeptide form. The di- or polypeptides mayalso contain an alanine, and those prepared with alanine, phenylalanine,or alanine derivatives, are preferred.

In one embodiment of the invention, the asymmetric carbon atoms in thehistidine-containing peptide is a catalyst in the D configuration,although the L-configuration in the histidine containing peptide is alsouseful. Choice of chirality in the catalyst can be made so as to providethe chirality desired in the product.

Functional groups in the amino acid catalyst can contain protectinggroups; any conventional amino acid protecting group known in the artcan be used. For example, the protecting group is an organic acid in thecase of the free N--H or an alcohol in the case of the free COOH. Anyorganic acid and alcohol which will not interfere with the reaction canbe used as the protecting group. Preferably, the protecting group isanother amino acid. Any amino acid can be used, but, preferably, theamino acid is non-heterocyclic and is a monoamino or diamino-alkanoic oraralkanoic acid, such as alanine, phenylalanine, glutamic acid, glycineand the like.

Acid addition salts of the amine catalysts are formed with any acid thatwill not interfere with the reaction. Suitable inorganic acids includehydrohalogenic acids, such as hydrochloric or hydrobromic; sulfur acids,such as sulfuric or toluenesulfonic; and phosphorus acids, such asphosphoric or phenylphosphonic; and organic acids, such as oxalic acidand the like, are also suitable to form the salts.

When preparing the di- or polypeptide catalyst also having an alanine(containing moiety), it is prepared from alanine or its derivatives;this includes alanine, beta-aminoalanine, beta-phenylalanine,3,4-dihydroxyphenylalanine and the like. When preparing the catalystfrom a histidine (containing moiety, including substituted histidines),it is preferably histidine, 3-methylhistidine, 1-methylhistidine,1-ethylhistidine, 1-propylhistidine, or 1-benzylhistidine and the like.Very good results are obtained when 1-methylhistidine is the moiety.Preferably, the catalyst is a cyclic dipeptide containing a histidinemoiety and an alanine moiety.

The peptide adducts (reaction produced) with ketene are novel andcomprise another aspect of the invention. They are prepared to containfrom about one mole to three moles of a ketene per mole of peptide and,preferably, about two and especially about one mole of ketene with a(cyclic) dipeptide. Obviously, it is preferable to form the adduct insitu with the non-symmetrical ketene reactant of the process, which isdescribed below under process conditions. However, treatment of theoptically-active catalyst with about 1.1 to 5 moles of a ketene,preferably in the absence of a solvent or any solvent used in preparingthe ketene, is suitable. The ketene may also be a similar kind butsymmetrical ketene, e.g. dimethyl ketene, diphenyl ketene or keteneitself.

Non-limiting examples of the optically-active histidine-containingcatalyst include histidine, alpha-methylhistidine, 1-methylhistidine,cyclo(histidyl-histidine), (benzyloxycarbonylalanyl)histidine methylester, cyclo(alanyl-histidine), cyclo(beta-phenylalanyl-histidine),cyclo(beta-phenylalanyl-1-methylhistidine),cyclo(beta-phenylalanyl-3-methylhistidine), histidine methyl esterhydrochloride, histidine ethyl ester dihydrochloride, anserine,cyclo(valyl-histidine), glycyl-histidine,cyclo(phenylalanyl-glycyl-histidine), cyclo(leucyl-histidine),cyclo(homophenylalanyl-histidine), cyclo(phenylalanyl-methylhistidine),N-alpha-(beta-naphthoyl)histidine, histidyl-alanine,histidyl-phenylalanamide hydrochloride, histidyl-phenylalanine,cyclo(histidyl-proline), cyclo(glycyl-histidine) in free or protectedform or a reaction product of these materials with a ketene. Also,cyclo(beta-phenylalanyl-histidine),cyclo(beta-phenylalanyl-1-methylhistidine) orcyclo(beta-phenylalanyl-3-methylhistidine) adduct with(4-(difluoromethoxy)phenyl)isopropylketene, histidine adduct withketene, cyclo(glycyl-histidine) adduct with(4-(difluoromethoxy)phenyl)isopropylketene or histidyl-alanine adductwith dimethylketene and the like.

In one subclass of the invention, the peptide catalyst has the formula##STR7## wherein X is H, alkyl or ##STR8## each R is independently alkylor cycloalkyl of up to 7 carbon atoms, optionally substituted phenyl,benzyl or the like, each of the n units of ##STR9## is independentlysubstituted in which Y is hydrogen, acyl, alkyl, or aralkyl of up to 10carbon atoms; Z is the residue of common amino acids that do notinterfere in the process of the invention including benzyl,3-carboxypropyl, 3-aminopropyl, mercaptomethyl, 4-hydroxybenzyl,imidazol-4-ylmethyl; each m is 0 or 1, n is 2 l to 16; when each m is 0,the catalyst has a cyclic structure denoted by the dotted line; with theproviso that at least one histidine or substituted histidine unit isincluded in the catalyst; or reaction products of the above catalystswith one to three moles of ketene.

When the peptide catalysts are prepared by conventional methods in thepresence of water, they can, if solid, also contain water ofcrystallization. The optically-active, nitrogen-based amino acid, e.g.,histidine-containing peptide, catalyst of the invention, thus, includesthe presence or absence of water of crystallization when solid.

Alternatively, the process of the invention comprises treating thenon-symmetrical ketene as previously defined with an aldehyde or ketoneand a source of cyanide ions in the presence of the optically-activecatalyst previously defined.

Any aldehyde or ketone (carbonyl compound) is useful (provided it doesnot contain substituent groups that form other stable reaction productswith cyanide ions or with the catalyst). Preferably, the aldehyde orketone has the formula IV ##STR10## wherein R³ is an optionallysubstituted hydrocarbyl or heterocyclic group and R⁴ is an optionallysubstituted hydrocarbyl group or a hydrogen atom, or, alternatively, R³and R⁴ together with the carbon atom to which they are attached form acarbocyclic group.

The hydrocarbyl groups represented by R³ and R⁴ in the formula IV maybe, for example, an alkyl, a cycloalkyl or an aryl group of up to 20carbon atoms, preferably up to 10 carbon atoms, or R³ in the formula IVmay be a carbocyclic or an O or S heterocyclic aryl group. Examples ofcarbocyclic aryl groups are phenyl, 1-naphthyl, 2-naphthyl and 2-anthrylgroups. Heterocyclic aromatic groups are derived from hetero-aromaticcompounds which are defined as in Kirk-Othmer, "Encyclopedia of ChemicalTechnology", Second Edition, Volume 2 (1963), page 702: obtained byreplacement of one or more carbon atoms of a carbocyclic aromaticcompound by a heteroatom selected from O or S--and also include thoseheterocyclic compounds having five-membered rings which show aromaticcharacteristics and are mentioned on page 703 of said volume. Suchaldehydes and ketone compounds are described in U.S. Pat. No. 4,132,723.Optional substituents include one or more of halogen atoms having anatomic number of from 9 to 35, inclusive, or an alkyl, alkenyl or alkoxygroup containing 1 to 6 carbon atoms, each optionally substituted by oneor more halogen atoms, or optionally substituted phenoxy, phenyl, benzylor benzoyl and equivalent kinds of substituents.

Preferably, an aromatic aldehyde is used of the formula ##STR11##wherein each A is independently a hydrogen atom, a halogen atom havingan atomic number of from 9 to 35, inclusive, or an alkyl, alkenyl oralkoxy group containing 1 to 6 carbon atoms, each optionally substitutedby one or more halogen atoms having an atomic number of from 9 to 35,inclusive; B is a hydrogen atom, a halogen atom having an atomic numberof from 9 to 35, inclusive, or an alkyl, alkenyl or alkoxy groupcontaining 1 to 6 carbon atoms, each optionally substituted by one ormore halogen atoms having an atomic number of from 9 to 35, inclusive;or is a group ##STR12## in which Y is O, CH₂, or C(O); m is 0 or 1 and Dand E each independently is a hydrogen atom, a halogen atom having anatomic number of from 9 to 35, inclusive, or an alkyl, alkenyl or alkoxygroup containing 1 to 6 carbon atoms, each optionally substituted by oneor more halogen atoms having an atomic number of from 9 to 35,inclusive.

Preferably, an aldehyde is used corresponding to thealpha-hydroxynitrile previously defined and, thus, has the formula##STR13## wherein A, D, E and Y have the same meanings as given in theformula above.

Examples of suitable aldehydes of the formula above include3-phenoxybenzaldehyde, 4-fluoro-3-phenoxybenzaldehyde and the like.

The source of cyanide ions is hydrogen cyanide or agent which generateshydrogen cyanide, such as a simple alpha-hydroxynitrile such as acetonecyanohydrin, under the reaction conditions. The molar ratio of hydrogencyanide to aldehyde or ketone is from about 1.0 to about 3.0 moles permole of aldehyde or ketone and, preferably, from about 1.1 to about 2.0.

The preparation of the cyanomethyl esters is conducted by adding thenon-symmetrical ketone to the alpha-hydroxynitrile, or to the aldehydeor ketone and a source of cyanide ions, dissolved in a solventcontaining the optically-active, e.g., D-histidine-containing peptidecatalyst, agitating the mixture, e.g., by stirring, and maintaining thereaction conditions for an amount of time to effect the formation of theoptically-active ester. Separation and recovery of the optically-activeester product are achieved by conventional techniques, includingextraction and the like.

The amount of catalyst can vary. For example, it can be used in therange of from about 0.01 to about 5 mole percent based upon the weightof the alpha-hydroxynitrile, aldehyde or ketone present, preferablyabout 0.1 to about 2.5 mole percent.

The molar ratio of the starting materials, non-symmetrical ketene andalpha-hydroxynitrile, aldehyde or ketone can vary. For example, themolar ratio of ketene to alpha-hydroxynitrile is from about 5:1 to about1:5 and, preferably, from about 2:1 to about 1:2. However, it isdesirable to have a molar excess of ketene to alpha-hydroxynitrile,aldehyde or ketone of from about 1:1.1 to about 1:1.5

The temperature of the reaction as well as the pressure can vary. Atnormal pressures, the temperature is from about 10° C. to about 50° C.,more or less. Ambient temperatures of about 0° C. to about 35° C. areconvenient, and temperatures of about 0° C. to about 15° C. arepreferred.

The alpha-hydroxynitriles and their corresponding aldehydes or ketonesare generally known in the literature. They can be either directlysynthesized chemically or often enzymatically or, in the case ofoptically-active alpha-hydroxynitrile, resolved by methodsconventionally known in the art, including those described in U.S. Pat.Nos. 3,649,457 and 4,273,727, Oku et al., J.C.S. Chem. Comm., pages229-230 (1981) and Becker et al., J. Amer. Chem. Soc., 88, pages4299-4300 (1966) and the like.

The optically-active alpha-hydroxynitriles, particularly in theS-configuration, are prepared by treating the corresponding aldehyde orketone with hydrogen cyanide in a solvent (such as hydrocarbon, etherand the like, preferably the same as used in the reaction of the productalcohol with the non-symmetrical ketene) and in the presence of acyclo(D-phenylalanyl-D-histidine) dipeptide catalyst. Such preparationof S-alpha-hydroxynitrile is disclosed and claimed in U.S. patentapplication Ser. No. 443,763, filed Nov. 22, 1982, abandoned, which isincorporated by reference and discussed below.

The catalyst is prepared by conventional peptide synthesis, for example,as in Greenstein, J. P. and M. Winitz, "Chemistry of the Amino Acids",John Wiley & Sons, Inc., New York, 1961. They can be recovered byextraction with acid followed by neutralization with a base.

In one embodiment of the process for preparing optically-activealpha-hydroxynitriles from aldehydes or ketones, the catalyst comprisinga solid cyclo(D-phenylalanyl-D-histidine) orcyclo(L-phenylalanyl-L-histidine) having a substantially non-crystallinecomponent as claimed in co-pending U.S. Ser. No. 535,500, filed Sept.26, 1983, and also described below.

In other words, the catalyst has a component having a substantiallyamorphous or non-crystalline structure. While the precise form of thiscyclo(D-phenyalanyl-D-histidine) or cyclo(L-phenylalanyl-L-histidine)dipeptide is not known, it appears that in the activated (amorphous ornon-crystalline) form, a number of the available --NH groups in thedipeptide are free of intermolecular hydrogen bonding to the available--C═O groups of the dipeptide crystal lattice as compared to the lessactive (crystalline component) form. This is believed to involve theformation of a less bonded linear or planar (or sheet) form of peptidestructure as opposed to the highly bonded ribbon (or chain) form ofpeptide structure because of the increase in the number of --NH groupsfree of intermolecular hydrogen bonding to available --C═O groups in thedipeptide lattice. Such being the case, the degree of amorphousness ornon-crystallinity is most readily determined by X-ray diffraction.

The wide-angle X-ray scattering (WAXS) measurements were carried out inreflection by means of a Philips APD3600/02 automated X-raydiffractometer. The samples were scanned at 20° C. in air from 5.0° to60.0° 2θ at 0.02 degree increments, and 0.6 second time increments withCu Kα radiation (40 KV, 35 ma).

The percent crystallinity was determined by a modified Hermans andWeidinger method (P. H. Hermans and A. Weidinger, Makromol. Chem., 50,98 (1961)). The diffuse background scattering below the main peaks wasconstructed assuming a linear baseline between 5°≦2θ≦60° andapproximating the amorphous scattering with a smooth curve. The X-raycrystallinity, W_(c), was calculated from the integrated crystalline andamorphous intensities F_(c) and F_(a) by the equation W_(c) =F_(c)/(F_(c) +F_(a)). The various definitions can be found in the text H. P.Klug and L. E. Alexander, X-Ray Diffraction Procedures forPolycrystalline and Amorphous Materials, Wiley-Interscience, New York,(1974).

As used herein the terms "amorphous" or "non-crystalline" define activecatalyst materials which have an amorphous or non-crystalline componentas determined by the area of the X-ray diffraction spectra obtained bythe method described above. Preferably, the "amorphous" or"non-crystalline" component of the materials as defined by the X-raydiffraction spectra is about 45% to about 65% or higher. Preferably, the"amorphous" or "non-crystalline" component is about 65% or higher.

The catalysts are also analyzable by photomicrographs in whichinefficient catalysts consist of agglomerates of fine crystallites.Crystallites are not evident in photomicrographs of active catalysts,which when, for example, are spray-dried, take the form ofhollow-appearing spheres.

The solid catalyst can be recovered by extraction with acid followed byneutralization with a base or preferably by treating with (dissolvingin) a solvent, for example a hydroxylic solvent, including loweralkanols of 1 to 10 carbon atoms such as isopropanol or preferablymethanol (preferably with heating, e.g. to reflux or quick flash), andreprecipitating (preferably below ambient temperature) which produces aless crystalline (or more amorphous) catalyst structure.

While it is preferred to directly prepare the catalyst of the presentinvention having the non-crystalline component, it is also within thescope of this invention to prepare a substantially crystalline catalystand to subsequently activate the catalyst by converting at least part ofthe crystalline material to an amorphous form. Thus, the presentinvention is directed to both a method of directly preparing an activecyclo(D-phenylalanyl-D-histidine) or cyclo(L-phenylalanyl-L-histidine)dipeptide catalyst and to a method of activating a crystalline catalystof this type, which methods both involve reducing or preventing theformation of a substantially crystalline form thereof. In the case ofactivation of a crystalline catalyst, the crystalline form is firstbroken down and then prevented at least in part from reforming.

It is believed that the breakdown of or the prevention of the formationof a number of intermolecular bonds between the amino N--H and thecarboxyl C═O groups in the crystal lattice makes the catalyst have anamorphous or non-crystalline form. In any event, an ordered depositionof crystals of the catalyst is discouraged or reduced.

Any means which will accomplish this reduction or prevention eitherduring the catalyst preparation or an after treatment are within thescope of the invention. Among the illustrative examples of methods whichreduce or prevent the formation of a highly crystalline form or highlyordered arrangement are (a) very rapid evaporation of a solution of thecatalyst, in the presence or absence of impurities or crystallinityinhibitors; (b) rapid precipitation of the catalyst from solution bydilution in a poor solvent; (c) freeze drying of a solution of thecatalyst; (d) rapid cooling of the melted catalyst in the presence orabsence of impurities or crystallinity inhibitors; (e) use ofcrystallinity inhibitors during solidification; and the like.

The unactivated dipeptide catalyst, when recovered at the end of aconventional synthesis process, is often almost completely inactive inthe cyanohydrination reaction, apparently because it has become highlycrystalline as can be determined by X-ray diffraction. Activation, asused herein, appears to involve converting at least part of the normallycrystalline material into an amorphous form such that the dipeptide isswelled by the reaction mixture and the chiral base function of thecatalyst is made accessible to the reactants. In order to produce highchirality in the cyanohydrination product, it appears that the catalystshould preferably be essentially insoluble in the cyanohyrinationsolvent.

The first step in converting what is or what normally would be acrystalline material to an amorphous form is to break down (or prevent)formation of the intermolecular bonds in the crystal lattice. Thebreakdown readily occurs when the material is melted or dissolved in asolvent. Once this has been accomplished, a method is used that willallow the separation of the dissolved material from the solvent at arate such that normal crystallization cannot occur. There are a numberof ways in which this might be effected: (a) rapid evaporation of thesolvent, e.g. as in a spray dryer; (b) rapid precipitation of thematerial by pouring a solution of it into a large volume of a differentsolvent that is miscible with the original solvent but does notdissolve, to a large extent, the material to be precipitated; (c) rapidfreezing of a solution followed by sublimation of the solvent (freezedrying); (d) rapid cooling of the melted catalyst; and (e) use ofinhibitors alone or with any of the above methods (a)-(d). Preferably,the method used is (a) rapid evaporation of the solvent and, especially,by means of spray drying.

Because of the polar nature and high melting point (˜250° C.) ofcyclo(D-phenylalanyl-D-histidine) or cyclo(L-phenylalanyl-L-histidine),the choice of solvents that will dissolve it to any appreciable extentis very limited. Potential solvents suitable and unsuitable that havebeen tested include those listed in Table 1 in order of decreasingeffectiveness, and the use of these will be discussed below in relationto the method of catalyst activation via recovery techniques or specificsubsequent activation treatment.

                  TABLE 1                                                         ______________________________________                                        SOLVENTS TESTED FOR SOLUBILITY OF                                             CYCLO (D-PHENYLALANYL-D-HISTIDINE)                                            Solvent      B.P./°C.                                                                        Solvency                                                ______________________________________                                        Dimethyl Sulfoxide                                                                         189      Good (5-10% w)                                          Acetic Acid  118      Good                                                    Formamide    210      >2.3% at 25° C.                                  1-Methyl-2-pyrroli-                                                                        202      >2.2% at 25° C.                                  dinone                                                                        Dimethylformamide                                                                          153      Fair to Good, <5% at 90° C.                      Liquid Ammonia                                                                             -33      ˜2% at -40° C.                             N--methylformamide                                                                         185      >2.4% at 25° C.                                  Methanol      64      1% w Hot, 0.3% w at 25° C.                       Water        100      Fair to Poor, 0.1% at 25° C.                     ______________________________________                                    

The use of crystallization inhibitors is an alternative method ofreducing or preventing the crystalline form of the dipeptide. Manychemicals can be used. It is useful if the crystallization inhibitor hasa similar kind of structure or has one or more substituents similar inkind to those found in the dipeptide, but the inhibitor is not identicalto the units of the dipeptide. In the case of this dipeptide, usefulkinds of crystallization inhibitors include those materials containing a--N--H and/or --C═O group, including ureas, aldehydes and amines. Evenby-product impurities of the dipeptide process containing suchsubstituents are useful crystallization inhibitors, e.g. making animpure product can make a more active catalyst.

The amount of catalyst used in making the S-alpha-hydroxynitrile canvary. For example, it can be used in the range of from about 0.1 toabout 10 mole percent based upon the weight of the aldehyde present,preferably about 1.0 to about 7.5 mole percent. The catalyst ispreferably well dispersed in the reaction mixture.

When the catalysts are prepared by conventional methods in the presenceof water, they can, if solid, also contain solvent (e.g. water) ofcrystallization. The optically-active, D-histidine-containing peptidecatalyst of the invention used to prepare the optically-activealpha-hydroxynitrile thus includes the presence or absence of solvent(e.g. water) of crystallization when solid.

The non-symmetrical ketenes used to prepare the optically-active estersare generally known in the art or are novel. Ketenes used in the presentinvention can be prepared by treating the corresponding acid halide witha tertiary amine.

Suitable tertiary amines include alkyl, aryl or heterocyclic tertiarynitrogen base including mono- or polyamines and the like. Preferably,the tertiary amine is an amine in which any alkyl groups contain from 1to 10 carbon atoms, any aryl or aralkyl groups contain from 6 to 20carbon atoms and 1 to 2 hydrocarbyl rings, and any heterocyclic aminescontain at least one ring nitrogen atom in a 5 or 6 memberedheterocyclic ring optionally containing a sulfur or oxygen atom oranother nitrogen atom, such as trimethylamine, triethylamine,tri-n-propylamine, pyridine and the like. Desirably, a tertiary aminecontains three alkyl groups of 1 to 4 carbon atoms, for example:trimethylamine, tri-n-propylamine, and especially triethylamine ortrimethylamine.

The reaction to prepare the non-symmetrical ketene is conducted in thepresence or absence of a solvent. When a solvent is used the solvent ispreferably a non-hydroxylic solvent such as hydrocarbons, chlorinatedhydrocarbons, ethers and the like. For example, suitable solvents arealkanes containing from 5 to 10 carbon atoms such as n-pentane,n-hexane, n-heptane, n-octane, n-nonane, n-decane and their isomers.Petroleum fractions rich in alkanes are also suitable, for example,gasoline with a boiling range at atmospheric pressure of between 40° and65° C., between 60° and 80° C. or between 80° and 110° C. Petroleumether is also suitable. Cyclohexane and methylcyclohexanes are examplesof useful cycloalkanes containing from 6 to 8 carbon atoms. Aromatichydrocarbon solvents can contain from 6 to 10 carbon atoms, for example,benzene, toluene, o-, m- and p-xylene, the trimethylbenzenes,p-ethyltoluene and the like. Suitable chlorinated hydrocarbons containfrom 1 to 4 chlorine atoms in combination with an alkane chaincontaining from 1 to 4 carbon atoms or with a benzene ring, for example,carbon tetrachloride, chloroform, dichloromethane, 1,2-dichloroethane,trichloroethane, perchloroethane, chlorobenzene and 1,2- or1,3-dichlorobenzene and the like. Ethers are generally those containingfrom 4 to 6 carbon atoms such as diethyl ether, methyl tert-butyl etherand diisopropyl ether and the like. Tetrahydrofuran and dioxane are alsouseful.

In the preparation of the non-symmetrical ketene, the molar ratio of thestarting materials can be varied widely. For example, the molar ratio ofacid halide to base is from about 10:1 to about 1:10, and preferablyfrom about 5:1 to about 1:5. However, it is desirable to have a molarexcess of base to acid halide. Therefore, a molar ratio of acid halideto base is desirably from about 1:1 to about 1:5 and conveniently fromabout 1:1.2 to about 1.2.

In the preparation of the non-symmetrical ketene, the temperature can bevaried widely. At normal pressure, for example, the temperature ofreaction can be varied but is preferably, for example, from about 10° C.to 40° C. more or less, although higher temperatures of up to about 75°C. to about 95° C. have been found very useful.

Separation and recovery of the product non-symmetrical ketene areachieved by conventional methods, including crystallization and thelike.

This process of the invention is useful for preparing non-symmetricalketenes from any acid halides which do not contain substituted groupswhich would react with the base. For example, the acid halide can bethat of an acyclic, alicyclic, aromatic or heteroaromatic acid.Preferably, the acid halide has the formula V ##STR14## wherein X is thehalogen atom, such as chlorine or bromine, R¹ and R² each independentlyis an alkyl, aralkyl, alkoxy, aryloxy, alkylthio, alkylsulfonyl,arylthio, or arylsulfonyl group containing from 1 to 10 carbon atoms ora cycloalkyl group containing 3 to 7 ring carbon atoms, or when takentogether with the carbon atom to which they are attached form anon-symmetrical cycloalkyl group containing 4 to 7 ring carbon atoms; R²is also an alkenyl or alkynyl containing from 2 to 10 carbon atoms; anaphthyl group; a phenyl group; a heterocyclic group containing 5 or 6ring atoms, one of which is oxygen, sulfur or nitrogen, and theremainder are carbon atoms, or is an amino group disubstituted by acyl,alkyl containing up to 10 carbon atoms, or a phenyl group. The R¹ and R²groups can be optionally substituted by one or more of halogen of atomicnumbers 9 to 35, an alkyl, haloalkyl or cycloalkyl group containing upto 7 carbon atoms, alkenyl or haloalkenyl group of 2 to 4, haloalkoxy oralkoxy group of 1 to 4 carbon atoms, haloalkylthio or alkylthio group of1 to 4 carbon atoms or equivalent kinds of substituents.

One class of acid halides are halides of pyrethroid acids, includingthose of U.S. Pat. Nos. 4,062,968 and 4,199,595. Examples of such acidhalides include those having the formula V in which R¹ is isopropyl orcyclopropyl, optionally substituted by one or more chlorine atoms; R² isan alkyl group containing 1 to 6 carbon atoms; an alkenyl groupcontaining 2 to 6 carbon atoms; a naphthyl group, a phenyl group or a(benzyloxycarbonyl)phenylamino group, each optionally ring-substitutedby one or more of halogen, alkyl, haloalkyl, alkoxy or haloalkoxy inwhich the halogens are bromine, chlorine or fluorine and the alkylgroups contain 1 or 4 carbon atoms. For example, the acid halide isisopropyl(4-chlorophenyl)acetyl chloride,isopropyl(4-(difluoromethoxy)phenyl)acetyl chloride,isopropyl((4-trifluoromethyl)-3-chlorophenyl)(benzyloxycarbonyl)amino)acetylchloride, and the like.

Preferably, in formula V, R¹ is isopropyl and R² is a phenyl groupoptionally substituted by halogen, an alkyl or haloalkyl group of 1 to 4carbon atoms or an alkoxy or haloalkoxy group containing 1 to 4 carbonatoms, preferably at the para position, especially useful are4-chlorophenyl, 4-(difluoromethoxyphenyl), 4-methylphenyl,4-tert-butylphenyl and the like.

Many of the non-symmetrical ketenes of the invention are known in theart per se, for example, (4-chlorophenyl)isopropylketene, as in U.S.Pat. No. 4,199,527. Some other non-symmetrical ketenes are believed tobe novel, for example, including(4-(difluoromethoxy)phenyl)isopropylketene.

The cyanomethyl esters for which the optically-active form is preparedby the process of the invention, i.e. of formula I ##STR15## aregenerally known in the art, including from Francis et al., J. Chem.Soc., 95, pages 1403-1409 (1909) and the like, and in the optical forms,including U.S. Pat. Nos. 4,151,195, 4,239,777, 4,328,167 and 4,133,826,and British Pat. No. 2,014,137 and the like. Any of thealpha-cyanomethyl esters prepared can be hydrolyzed to theircorresponding acids by conventional hydrolysis methods known in the art.Preferably, the product optically-active ester isS-alpha-cyano-3-phenoxybenzyl S-alpha-isopropyl-p-chlorophenylacetate,S-alpha-cyano-3-phenoxybenzylS-alpha-isopropyl-p-(difluoromethoxy)phenylacetate, and the like.

ILLUSTRATIVE EMBODIMENTS Embodiment 1N-(Benzyloxycarbonyl)-D-phenylalanine

A 15.0 g sample of D-phenylalanine was dissolved in 45 ml of aqueoussolution containing 7.26 g of 50% sodium hydroxide. This solution wasstirred at 0°-10° C. as 16.3 g of benzyl chloroformate was added rapidlyin portions. The resulting reaction was mildly exothermic, and shortlyafter addition, solids precipitated. An additional 45 ml of water and3.63 g of 50% sodium hydroxide were added, causing most of the solids toredissolve. The reaction mixture was stirred for 20 minutes and thenacidified with 6N hydrochloric acid. The resulting solids were filtered,washed with water and then with hexane, and dried by suction and thenunder vacuum to give 47 g of white solids. These solids dissolved inether were washed twice with 1N hydrochloric acid and then with water,dried over MgSO₄ and stripped to 35° C. at 2.5 mm Hg to give 27.7 g ofthe desired product as a colorless oil.

Embodiment 2 N-(Benzyloxycarbonyl)-D-phenylalanine, p-nitrophenyl Ester

A 300 ml three-neck flask with stirrer and dropping funnel was chargedunder a nitrogen atmosphere with 27 g of the acid of Embodiment 1 abovein 135 ml of pyridine, followed by 13.2 g of p-nitrophenol. Theresulting solution was cooled to 0° to 10° C. as 14.6 g of phosphorusoxychloride was added. The resulting mixture was warmed to 25° C.,stirred for 15 minutes, then poured into 300 ml of ice water. Filtrationof the resulting solid, followed by washing with water and drying bysuction, gave 33 g of product. This was crystallized from 340 ml of hotethyl alcohol with chilling to -5° C. The product was filtered, washedwith chilled ethyl alcohol, then with hexane, and sucked dry to give28.7 g of the desired product, m.p. 122.5°-124.5° C., [α]_(D) ²³ +24.7(c 2.0, dimethylformamide).

Embodiment 3 N-Benzyloxycarbonyl-D-phenylalanyl-D-histidine Methyl Ester

To a stirred solution of 5.0 g of D-histidine methyl ester hydrochloridein 40 ml of methylene chloride was added 4.18 g of triethylaminefollowed by 8.27 g of the nitrophenyl ester prepared as in Embodiment 2above. The reaction mixture immediately became bright yellow and solidsbegan to precipitate. The reaction mixture was stirred for 2 hours, thenstored overnight at -10° C. The reaction mixture was rewarmed to roomtemperature, and 0.6 ml of triethylamine was added. Then, 490 mg of theD-histidine methyl ester hydrochloride was added, and stirring wascontinued for 2 hours. The reaction mixture was washed with 20 ml ofwater, then twice with 20 ml of 10% ammonium hydroxide, and then twicewith 20 ml of water. All the washes were back-extracted serially with 20ml of methylene chloride, and the combined organic phases were driedwith MgSO₄ and stripped to 100 ml, filtered through silica, followed by25 ml of 20% methanol in ethyl acetate. The resulting eluate wasstripped to 40 ml and diluted to 120 ml with diethyl ether; theprecipitated solid was filtered, washed with diethyl ether, and dried bysuction to give 5.66 g of the desired product as a white solid, m.p.114.5°-117° C. [α]_(D) ²⁰ -55.5 (c 2 in CHCl₃).

Embodiment 4 Cyclo(D-phenylalanyl-D-histidine)

5.60 g of methyl ester of Embodiment 3 above was stirred andhydrogenated in 100 ml of methanol over 220 mg of 10% palladium oncarbon at atmospheric pressure. After 3 hours, solids began toprecipitate; an additional 25 ml of methanol was added to facilitatestirring. After 7 hours, an additional 280 ml of methanol was added asthe mixture was heated to reflux. The mixture was filtered hot, and thefiltrate was stripped to a gel-mush and mixed with 100 ml of diethylether. The resulting solid was filtered, washed with diethyl ether, anddried by suction and then under high vacuum at 35° C. to give 3.29 g ofthe desired product as an off-white powder, [α]_(D) ²³ =+68.5 (c 2.0 inCH₃ COOH).

Embodiment 5 (4-Chlorophenyl)isopropylketene

To a solution of 2.31 g of isopropyl(4-chlorophenyl)acetyl chloride in10 ml of methylene chloride was added in one portion 1.5 g oftriethylamine. After 18 hours, 15 ml of heptane was added to the mixtureand the triethylamine hydrochloride was removed by filtration. Thefiltrate was stripped and 10 ml of heptane was added and the resultingmixture was filtered and stripped to give a yellow residue, which wasdissolved in 5 ml heptane for GLC analysis. The resulting solution wasdistilled through a Bantam-ware short-neck head from an oil bath at125°-150° C. and head temperature of 110°-100° C. at 0.2-0.05 mm to give0.95 g of distillate and 0.81 g of gum. The distillate was crystallizedtwice from 2 volumes of hexane at -80° C. The solid was melted andstripped to about 40° C. at 0.5 mm to give 0.42 g of the desired productas a yellow liquid.

Embodiment 6 (4-Chlorophenyl)isopropylketene

A sample of 53.2 g of isopropyl(4-chlorophenyl)acetic acid was treatedwith 21.5 ml of thionyl chloride in a 500 ml flask and heated slowly to80° C. and maintained at 80° C. for 20 minutes. The reaction mixture wasallowed to stand at room temperature for 2 days. The volatiles werestripped to 75° C. at 0.5 mm Hg. The resulting yellow liquid was dilutedwith 250 ml of methylene chloride followed by addition of 38.0 g oftriethylamine. The mixture was stirred until triethylamine hydrochloridebegan to precipitate after 30 minutes. After 16 hours, the reactionmixture was filtered and solid triethylamine hydrochloride was washedwith heptane. Most of the solvent was stripped from the filtrate byrotary evaporation at 50° C. The residue was diluted with 75 ml ofheptane and additional triethylamine hydrochloride was removed byfiltration as above. The filtrate was restripped and rediluted with 75ml heptane and refiltered with the aid of 25 ml of heptane. The filtratewas cooled in dry ice, seeded and crystallized. The resulting crystalswere filtered with a filter stick and washed with chilled heptane. Thefiltered solids were melted, diluted with one-half volume heptane,crystallized at -80° C. and the collected solid was melted and stored at-80° C. The filtrate solution was warmed, stripped of most solvent, thendistilled through a Bantam ware short path head at 0.05 to 0.06 mm Hgfrom an oil bath at 90°-120° C. Total distillate was 14.5 g collected asa bright yellow-orange liquid at a head temperature of 60°-85° C. Thedistillate was crystallized from an equal volume of pentane at -80° C.,filtered and washed twice with heptane as above to give, on warming, asecond melt. The stripped filtrates totalling 5.79 g were crystallizedas above in a 6-inch test tube and the melt was recrystallizedimmediately as described above to give a third melt. The three meltswere combined and stripped to 50° C. at 5 mm Hg to give 29.4 g of thedesired ketene as a yellow liquid.

Embodiment 7 (4-Chlorophenyl)isopropylketene

To 57.75 g of isopropyl(4-chlorophenyl)acetyl chloride was added 69.4 mlof triethylamine. The mixture was allowed to stand overnight at 20° C.The resulting mushy solid was crushed, diluted with 300 ml ofredistilled hexane and filtered. The solids were washed three times with75 ml of hexane, filtered and dried by suction with calcium chloridedried air to give 32 g triethylamine hydrochloride. The combined hexanesolutions of ketene slowly deposited additional solids; the mixture waslet stand at room temperature overnight with the flask wrapped inaluminum foil and filtered again to give 0.75 g of additional solids.The solvent was removed from the filtrate by rotary evaporation, thentaken briefly to 1 mm Hg. To the mixture was added 500 ml of hexane, andafter filtration, the filtrate was stripped to a yellow oil. This oilwas distilled through a Bantam-ware short path head at 0.5 mm Hg to give28.61 g of the desired ketene as a yellow liquid, d²⁰ 1.10.

Embodiment 8 (4-(Difluoromethoxy)phenyl)isopropylketene

Following procedures similar to those described in Embodiment 7 above,the desired product is prepared by treatingisopropyl(p-(difluoromethoxy)phenyl)acetyl chloride with triethylamine.

Embodiment 9 S-alpha-Cyano-3-phenoxybenzyl Alcohol

A 100 ml three-neck Bantam-ware flask was charged with 43 mg ofcyclo(D-phenylalanyl-D-histidine) and put under a nitrogen atmosphere.Then, 3.51 ml of hydrogen cyanide was added by syringe causing thecatalyst to swell and become a gel. After 5 minutes, 30 ml of toluenewas added, causing additional catalyst to precipitate. 5.95 g of3-phenoxybenzaldehyde was added all at once. The reaction mixture wasstirred for 4.75 hours and then quenched with 20 ml of water containing10 drops of concentrated hydrochloric acid. The toluene solution wasseparated, washed twice with water, and diluted to 50 ml with toluenefor analysis, which showed 80% S-alpha-cyano-3-phenoxybenzyl alcoholisomer was produced.

Embodiment 10 S-alpha-Cyano-3-phenoxybenzyl Alcohol

The reaction of Embodiment 5 above was repeated using 171 mg ofcyclo(D-phenylalanyl-D-histidine). At intervals, 0.25 ml samples wereremoved and examined by gas liquid chromatography as follows:

    ______________________________________                                        Time        % Conversion of Aldehyde                                          ______________________________________                                        35     minutes  20                                                            2      hours    76                                                            6.5    hours    95                                                            ______________________________________                                    

After 7 hours, the reaction mixture was quenched by addition of 10 ml of1N hydrochloric acid. The organic phase was separated and washed twicewith water, dried over MgSO₄, filtered and stored at -10° C. Thefiltrate was diluted to 50 ml with toluene and the optical rotation wasdetermined to be -1.54° at 21° in 1 dm cell. A sample of the product wasacetylated with p-nitrophenylacetic anhydride and the stereoisomer ratiowas determined by HPLC on a chiral Pirkle column to be 71%S-alpha-cyano-3-phenoxybenzyl alcohol and 29%R-alpha-cyano-3-phenoxybenzyl alcohol.

Embodiment 11 S-alpha-Cyano-3-phenoxybenzyl Alcohol

Two small round-bottom flasks having magnetic stirrers and septum coverswere each charged with 22.5 mg of cyclo(D-phenylalanyl-D-histidine) andput under nitrogen. A sample of 0.98 ml of hydrogen cyanide was dilutedto 25 ml with toluene and 5 ml of the solution was added via syringe toeach flask. After about 5 minutes, 0.87 ml of 3-phenoxybenzaldehyde(POAL) was added to each flask. Flask No. 1 was stirred in an oil bathat 35° C. and flask No. 2 was stirred in a water bath at 24°-26° C. Theresults of these experiments are below.

    __________________________________________________________________________    Flask No. 1          Flask No. 2                                              Time,     α-Hydroxy- α-Hydroxy-                                   hr  POAL, %                                                                             nitrile, %                                                                          R/S  POAL, %                                                                             nitrile, %                                                                          R/S                                          __________________________________________________________________________    0.5 19    81     8.7/91.3                                                                          18    82    15.8/84.2                                    1   12    88    --   13    87    14.4/85.6                                    2   12    88    --   12    88    --                                           4   10    90    11.4/88.6                                                                          12    88    19.0/81.0                                    8   10    90    --   13    87    --                                           __________________________________________________________________________

Embodiment 12 S-alpha-Cyano-3-phenoxybenzyl Alcohol

A reaction was conducted by contacting 0.0099 m/kgcyclo(D-phenylalanyl-D-histidine) with 0.99 m/kg of3-phenoxybenzaldehyde followed by 2.2 m/kg of hydrogen cyanide and 190ppm water. The reaction was conducted in toluene at 25° C. The productobtained with 93% conversion of aldehyde was 88%S-alpha-cyano-3-phenoxybenzyl alcohol isomer.

Embodiment 13 S-alpha-Cyano-3-phenoxybenzylS-Isopropyl(4-chlorophenyl)acetate

A 1 dram vial was charged with 1 ml of a solution ofalpha-cyano-3-phenoxybenzyl alcohol having an R/S ratio of ca 72/28, and0.121 ml of (4-chlorophenyl)isopropylketene. Then, 7.5 mg ofcyclo(D-phenylalanyl-D-histidine) was added. The reaction mixture wasstirred at ambient temperature for 24 hours to give a colorless productcontaining a white, insoluble floc. The reaction product was centrifugedto remove solids, washed with 1N hydrochloric acid and twice with water,dried with MgSO₄ and filtered and diluted to 2 ml with solvent foranalysis. The desired product had by Pirkle column analysis a ratio of55.1% S-alpha-cyano-3-phenoxybenzyl S-isopropyl(4-chlorophenyl)acetateand 16.6% R-alpha-cyano-3-phenoxybenzylR-isopropyl(4-chlorophenyl)acetate.

Embodiment 14 S-alpha-Cyano-3-phenoxybenzylS-Isopropyl(4-chlorophenyl)acetate

A 1 dram vial was charged with 1 ml of S-alpha-cyano-3-phenoxybenzylalcohol solution as described in Embodiment 13 followed by 0.121 ml of(4-chlorophenyl)isopropylketene and then 7.5 mg ofcyclo(D-phenylalanyl-D-histidine). The resulting mixture was stirred atambient temperature for 20 hours to give a colorless product liquidcontaining a white floc. This reaction product mixture was centrifugedand the insoluble cake of gel was washed and centrifuged 4 times with 1ml portions of hexane. The combined organic extracts were washed withdilute hydrochloric acid and water, dried, stripped to below 1 ml andthen diluted to 2 ml in toluene. The desired product had by Pirklecolumn analysis a ratio of 63.0% S-alpha-cyano-3-phenoxybenzylS-isopropyl(4-chlorophenyl)acetate and 12.5%R-alpha-cyano-3-phenoxybenzyl R-isopropyl(4-chlorophenyl)acetate.

Embodiment 15 S-alpha-Cyano-3-phenoxybenzylS-Isopropyl(4-chlorophenyl)acetate

The catalyst gel recovered from Embodiment 14 above was washed with 1.5ml of hexane and charged to a 1 dram vial. The vial was charged with 1ml of S-alpha-cyano-3-phenoxybenzyl alcohol solution as described inEmbodiment 14 and 0.121 ml of (4-chlorophenyl)isopropylketene. Thereaction mixture was stirred for 16 hours and then extracted 5 timeswith 1 ml hexane, and the combined extracts was stripped and diluted to2 ml in toluene for analysis. The desired product had by Pirkle columnanalysis a ratio of 62.4% S-alpha-cyano-3-phenoxybenzylS-isopropyl(4-chlorophenyl)acetate and 14.1%R-alpha-cyano-3-phenoxybenzyl R-isopropyl(4-chlorophenyl)acetate.

Embodiment 16 S-alpha-Cyano-3-phenoxybenzylS-isopropyl(4-chlorophenyl)acetate

A 0.5 dram vial containing a magnetic stirring bar and 4 mg ofcyclo(D-phenylalanyl-D-histidine) was filled with nitrogen and cappedwith a septum cap. Into this vial was injected 0.174 ml of3-phenoxybenzaldehyde followed by 0.044 ml of hydrogen cyanide. After 5minutes stirring, 0.18 ml of (4-chlorophenyl)isopropylketene was added.After 2 days, the reaction mixture was diluted with toluene, washed with1N hydrochloric acid, water, dried (MgSO₄) and filtered. A solutionthereof in 1 ml toluene was analyzed and determined to be enriched inthe desired material.

Embodiment 17

A Niro Atomizer laboratory spray dryer with a ca 31 inch diameterchamber was assembled. In operation, 40 SCFM N₂ is heated to 140° C. andfed to the dryer chamber. A warm solution of 0.5-1.0%wcyclo(D-phenylalanyl-D-histidine) in methanol is fed via a rotary vanedatomizer to the chamber above the N₂ inlet. The droplets ofcyclo(D-phenylalanyl-D-histidine) solution are rapidly dried to givehollow spherical particles of 1 to 10 μm diameter. The combined streamis fed to a cyclone where 50-70% of the particles are captured.

Six test runs were made using 5 to 10 gm ofcyclo(D-phenylalanyl-D-histidine) each. Starting with a catalyst thatwas inefficient for cyanohydrination, all the products were activated togive good reaction rate and produce (S)-alpha-cyano-3-phenoxybenzylalcohol with EE's between 75-80% at 97% conversion of3-phenoxybenzaldehyde. Water and sodium chloride, simulating recycleoperation, apparently had no effect on activation. On the other hand,the addition of urea to further disrupt crystallization ofcyclo(D-phenylalanyl-D-histidine) did not result in any furtherimprovement. The results of the six test runs are tabulated in Table 2.

Following procedures similar to those described in Embodiment 17 above,cyclo(L-phenylalanyl-L-histidine) is activated by spray drying.

                                      TABLE 2                                     __________________________________________________________________________    ACTIVATION OF CYCLO(D-PHENYLALANYL-D-HISTIDINE) FOR SPRAY                     __________________________________________________________________________    DRYING                                                                        Catalyst   Feed Composition (Rest MeOH)                                                                     Feed                                                                              N.sub.2                                                                            Temp                                         Purity                                                                             DDCAT.sup.d                                                                         H.sub.2 O                                                                         NaCl                                                                               Others                                                                            Rate                                                                              Rate In                                     Experiment                                                                          % w  % w   % w % w % w  ml/min                                                                            SCFM.sup.f                                                                         °C.                             __________________________________________________________________________    1     87.sup.                                                                            0.49               115 42   135                                    2     87.sup.                                                                            0.48               225 42   ˜160                             3     92.sup.b                                                                           0.84               125 43   135-140                                4     92.sup.b                                                                           0.63  4.5          110 43   139                                    5     92.sup.b                                                                           0.62  4.5 1.0      135 43   137-140                                6     92.sup.b                                                                           0.65  --  --  0.033                                                                              125 43   139                                    7     92.sup.b                                                                           0.80  --  --  --   135 42   135-140                                __________________________________________________________________________                              Cyanohydrination In                                                           Toluene at 25° C.                                  Temp                                                                              Atomizer                                                                           Catalyst                                                                            Particle                                                                              POAL.sup.e                                                                          (S)--POAL.CN.sup.e                               Out RPM  Recovery                                                                            Size Time                                                                             Conversion                                                                          Selectivity.sup.c                          Experiment                                                                          °C.                                                                        × 10.sup.-3                                                                  %     μm                                                                              hr %     %                                          __________________________________________________________________________    1     60-75                                                                             37   46    1-12 1  92.2  91                                                                   2  95.9  90                                                                   4  96.9  90                                                                   5.5                                                                              95.9  90                                         2     60-70                                                                             31   58    1-12 1  91.3  90                                                                   3  95.5  88                                                                   4  96.7  88                                                                   5.1                                                                              98.4                                             3     55-65                                                                             37   .sup. 66.sup.a                                                                      1-10 1  93    90                                                                   2  96.7  90                                                                   3  96.6  92                                                                   4  97.6  90                                         4     65-75                                                                             36   .sup. 56.sup.a                                                                      1-10 1  94.6                                                                       2  96.9  90                                                                   3  98.7  89                                         5     55-65                                                                             36   68    1-10 1  93.6  91                                                                   2  96.6  90                                                                   3  95.4  91                                                                   4  97.5  90                                                                   5        90                                         6     70-75                                                                             36   58    1-10 1  92.3  90                                                                   2  91.0  90                                                                   4  94.7  89                                                                   5  96.0  90                                         7     55-70                                                                             38   77    1-10 1  93.3  93                                                                   2  96.1  91                                                                   3  95.9  92                                                                   4  97.6  92                                                                   5  96.0  91                                         __________________________________________________________________________     .sup.a Mostly held in cyclone by static electricity.                          .sup.b 96% purity by pot. titration.                                          .sup.c EE = 2 (selectivity)  100, %.                                          .sup.d DDCAT = cyclo(Dphenylalanyl-D-histidine)                               .sup.e POAL = 3phenoxybenzaldehyde, (S)--POAL.CN =                            (S)--cyano-3-phenoxybenzyl alcohol.                                           .sup.f SCFM = standard cubic feet per minute.                            

Embodiment 18

Table 3 summarizes the results of tests and scale-up experiments toactivate the cyclo(D-phenylalanyl-D-histidine) catalyst by solventevaporation, most of which were from methanol. Whereas the catalystrecovered by conventional crystallization was not very active, rapidevaporation of methanolic solutions was rather effective in producingactive catalysts (Experiments 1-11). The addition of small amounts ofimpurities (5-10% basis catalyst) appeared to help prevent normalcrystallization (compare Experiment 1, have no impurity, to thosefollowing it in the table). Except for dimethyl sulfoxide, all of theadditives gave getter results than the base case. These experimentsinvolved rapid stripping of 25 ml of methanol from 0.2 g of catalyst ina rotating evaporator. Attempts to scale up Experiment 9 were onlypartially successful. The product from the first experiment had anactivity/enantiomeric excess of 88%/75%, as compared to 98%/88% in thesmaller experiment. The second of the large experiments was even lessactive, 75%/47%. Longer times required to strip off large volumes ofsolvent resulted in greater amounts of crystallization of the dipeptide,thus resulting in a less active material. A solution to this problem isto spray dry the solution so that the solids are recovered rapidly.Solvents that may be useful in this approach are methanol, liquidammonia, and acetic acid.

                                      TABLE 3                                     __________________________________________________________________________     ACTIVATION OF CYCLO(D-PHENYLALANYL-D-HISTIDINE)                              BY SOLVENT EVAPORATION                                                                                    Cyanohydrination.sup.a                                                    Temp                                                                              Conversion                                                                          Enantiomeric                                Experiment                                                                          Method of Evaporation                                                                           °C.                                                                        %/3 Hr                                                                              Excess, %                                   __________________________________________________________________________    1     Rapid small.sup.b evap. from meth-                                                              ˜0                                                                          83    79                                                anol                                                                    2     Rapid small evap. from methanol,                                                                ˜0                                                                          96    87                                                +5% urea                                                                3     Rapid small evap. from methanol,                                                                0-20                                                                              95    85                                                +10% 3-phenoxybenzyldehyde                                              4     Rapid small evap. from methanol,                                                                0-20                                                                              99    85                                                +10% M acetic acid                                                      5     Rapid small evap. from methanol,                                                                0-20                                                                              99    86                                                +10% CH.sub.3 CN                                                        6     Rapid small evap. from methanol,                                                                0-20                                                                              97    87                                                +10% α-isopropyl-p-chlorophenyl-                                        acetonitrile                                                            7     Rapid small evap. from methanol,                                                                0-20                                                                              95    75                                                +7% HIS--OME/triethylamine                                              8     Rapid small evap. from methanol,                                                                0-20                                                                              92    80                                                +50% water                                                              9     Rapid small evap. from methanol                                                                 0-20                                                                              98    88                                                +5% filtrate residue                                                    10    Rapid small evap. from methanol,                                                                0-20                                                                              16    31                                                +10% dimethyl sulfoxide                                                 11    Rapid small evap. from methanol,                                                                0-20                                                                              96    87                                                +5% Z--D-PHE--HIS--OME                                                  12    Slow Evaporation from hot                                                                       70-90                                                                             67    63                                                methanol/water                                                          13    Large run similar to 9 (15 g)                                                                       88    75                                          14    Large run similar to 9 (15 g)                                                                       75    47                                          15    Medium run similar to 9 (7 g in 2 Hr)                                                               98    86                                          __________________________________________________________________________     .sup.a Cyanohydrination of 3phenoxybenzyldehyde with HCN to give              (S)alpha-cyano-3-phenoxybenzyl alcohol.                                       .sup.b Small means 0.2 g of catalyst in 25 ml of solvent.                

Embodiment 19

Solvent precipitation is another way of activating thecyclo(D-phenylalanyl-D-histidine)dipeptide, and Table 4 summarizes someresults using this approach. In all but one example shown, dimethylsulfoxide (DMSO) was used to dissolve the catalyst as a 5% solution, andthe dipeptide was precipitated by pouring this solution into awell-stirred vessel of second solvent, under a variety of conditions. Inmost cases, the precipitated catalyst formed a voluminous gel which wasrinsed with the second solvent to remove dimethyl sulfoxide and blowndry. In Experiments 5-14 urea (5% basis catalyst) was added to the DMSOsolution to aid in preventing crystallization of the dipeptide. In anycase, from the results shown, it appears that (a) of the fiveprecipitating solvents tested, dichloromethane and toluene appeared tobe best; (b) high temperature (80° C.) gave better results than lowertemperature (25° C.); (c) high dilution gave a better result than lowerdilution (compare Experiments 5 and 6); and (d) the catalystprecipitated from liquid ammonia solution (Experiment 4) was moderatelyactive (82% conversion in 3 hours) and quite selective (84% EE, evenafter 22 hours of contact with the catalyst). Unlike all of the othersthis product was a dense solid that was easy to filter and wash. Anumber of solvents for cyclo(PHE-HIS) shown in Table 1 can be used inthis approach, namely, DMSO, acetic acid, formamide,1-methyl-2-pyrrolidinone, dimethylformamide, N-methylformamide, liquidammonia, and the like.

                                      TABLE 4                                     __________________________________________________________________________    ACTIVATION OF CYCLO(D-PHENYLALANYL-D-HISTIDINE)                               BY SOLVENT PRECIPITATION                                                                               Cyanohydrination.sup.d                                                        Conversion                                                                          Enantiomeric                                   Experiment                                                                          Method of Precipitation                                                                          %/3 Hr                                                                              Excess, %                                      __________________________________________________________________________    1     From dimethyl sulfoxide (5%) into                                                                65    41                                                   diethyl ether                                                           2     From dimethyl sulfoxide (5%) into                                                                97    72                                                   toluene, 80° C.                                                  3     From dimethyl sulfoxide (5%) into                                                                74    37                                                   toluene 25° C., large scale                                      4     From liquid NH.sub.3 (2%) into diethyl                                                           82    .sup. 84.sup.b                                       ether, -40° C.                                                   5     From dimethyl sulfoxide.sup.a into 20 V                                                          42    31                                                   toluene, 25° C.                                                  6     From dimethyl sulfoxide into 5 V                                                                  4    10                                                   toluene, 25° C.                                                  7     From dimethyl sulfoxide into 20 V                                                                85    57                                                   toluene, 80° C.                                                  8     From dimethyl sulfoxide into 20 V                                                                77    .sup. 37.sup.e                                       acetonitrile, 80° C./25° C.                               9     From dimethyl sulfoxide into 20 V                                                                 2     18.sup.f                                            acetonitrile, 25° C.                                             10    From dimethyl sulfoxide into 20V                                                                  2    .sup. 19.sup.g                                       tetrahydrofuran, 25° C.                                          11    From dimethyl sulfoxide into 20 V                                                                 2    .sup.  0.sup.c                                       diethyl ether, 25° C.                                            12    From dimethyl sulfoxide into 20 V                                                                77    49                                                   dichloromethane                                                         13    From dimethyl sulfoxide into 20 V                                                                77    60                                                   tetrahydrofuran + 1% v/v H.sub.2 O, 25° C.                       14    Experiment 13 and vacuum oven dried                                                              89    .sup. 50.sup.h                                 __________________________________________________________________________     .sup.a Catalyst 5% w/v in dimethyl sulfoxide, urea 5% basis catalyst.         .sup.b After 22 hours at 95% conversion.                                      .sup.c After 71 hours the enantiomeric excess was 24% at a conversion of      97%.                                                                          .sup.d Cyanohydrination of 3phenoxybenzaldehyde with HCN to give              (S)alpha-cyano-3-phenoxybenzyl alcohol.                                       .sup.e At 92% conversion.                                                     .sup.f At 44% conversion.                                                     .sup.g At 49% conversion.                                                     .sup.h After 4 hours.                                                    

Embodiment 20

Another method tested for activating the catalyst is freeze drying. Thisapproach requires a solvent for the dipeptide that freezes at aconvenient temperature and is volatile enough to be sublimed at belowthat temperature and at a practical pressure (vacuum). Of the solventstested, only water and acetic acid meet these requirements. The resultsof some of these tests are summarized in Table 5. Freeze drying of a0.1%w solution of the dipeptide in water gave an excellent product(Experiment 5). An attempt to freeze dry a solution in dimethylsulfoxide failed because the solvent was too high boiling to be sublimedat about 0° C. and 170 microns pressure. On the other hand, solutions inglacial acetic acid were readily freeze dried. The product from thisfreeze drying contains one mole of acetic acid per mole of catalyst. Inspite of this, the product was surprisingly active and selective(Experiment 2). This acid is relatively loosely held by the catalyst,and it was volatilized away in a sweep of air, on the one hand(Experiment 3), or neutralized by triethylamine treatment, on the other(Experiment 4). In both cases the products had about the sameactivity/selectivity: 93%/72%.

                                      TABLE 5                                     __________________________________________________________________________    ACTIVATION OF CYCLO(D-PHENYLALANYL-D-HISTIDINE)                               BY FREEZE DRYING                                                                                       Cyanohydrination.sup.c                                                        Conversion                                                                          Enantiomeric                                   Experiment                                                                          Solvent/Work Up    %/3 Hr                                                                              Excess, %.sup.b                                __________________________________________________________________________    1     From 2% solution in dimethyl sulfoxide                                                           --    --                                             2     From 1.9% solution in acetic acid                                                                74    56 (6.5)                                       3     Product from experiment 2 air swept                                                              93    73 (5)                                               2 days                                                                  4     Product from Experiment 2 treated with                                                           93    72 (6.3)                                             triethylamine in diethyl ether                                          5     From 0.1% solution in water                                                                      98    85 (2.5)                                       __________________________________________________________________________     .sup.a Solution frozen at -40° C.; solvent sublimed at 0.1 Torr.       .sup.b Numbers in parentheses indicate time, in hours.                        .sup.c Cyanohydrination of 3phenoxybenzaldehyde with HCN to give              (S)alpha-cyano-3-phenoxybenzyl alcohol.                                  

Following procedures similar to those described in Embodiment 21 above,cyclo(L-phenylalanyl-L-histidine) is activated by freeze drying.

Embodiments 21-103

A vial was charged with 13.5% w/v of racemic alpha-cyano-3-phenoxybenzylalcohol solution in 0.6M of toluene followed by a 5% w/v excess of(4-chlorophenyl)isopropylketene and 4 m% of a catalyst. The resultingmixture was stirred at 25° C. for a period of time until the reactionhad essentially gone to completion or was terminated.

The catalyst used and the predominant isomer are set forth in the Tablebelow in which the symbols used to describe the catalyst are standard inpeptide chemistry, e.g. as set forth in Schroder and Lubke, "ThePeptide", Vol. II, pages XI-XXVI (1966); and the isomers are Aα=S-acidS-alcohol isomer, Aβ=S-acid R-alcohol isomer, Bα=R-acid S-alcohol isomerand Bβ=R-acid R-alcohol isomer.

                                      TABLE                                       __________________________________________________________________________                                       %                                                                       Time  Predominant                                Embodiment                                                                           Catalyst              (hours)                                                                             Isomer                                     __________________________________________________________________________    21     cyc(2-pyridylala-L-Phe)                                                                              4    Bα = 29.8                            22     cyc(D-PheL-His)       <28   Bβ = 38.0                             23     cyc(L-TrpL-Trp)       >36   Bβ = 28.1                             24     ZL-LeuL-HisMe ester    6.5  Aα = 32.4                            25     D-Histidine (free base)                                                                             >36   Bβ = 30.0                             26     D-HisMe ester.2HCl     30   Aα = 29.3                            27     L-Phe                 >30   Aβ = 30.0                             28     SerMe ester.HCl       >36   Aα,Bβ = 27.0 each               29     cyc(L-LeuL-His)        30   Aα = 29.4                            30     cyc(GlyL-Trp)         >36   Bβ = 36.7                             31     cyc(D-PheD-Trp)       >52   Aβ = 36.7                             32     cyc(D-PheL-His)       <36   Bβ = 36.4                             33     cyc(L-PheL-Phe)       >52   Aβ, Bα = 27.8 each              34     cyc(L-PheL-Met)       >52   Bβ = 31.8                             35     cyc(D-PheD-His)        4    Aα = 40.7                            36     NAcetyl-L-His.H.sub.2 O                                                                              30   Bβ = 30.6                             37     ZD-PheL-His Me ester   28   Bβ = 28.5                             38     cyc(L-HomoPheL-His)   <18   Aα = 29.9                            39     cyc(L-PheL-3-MeHis)    1.5  Bβ = 35.8                             40     (L-Phe).sup.4.3H.sub.2 O                                                                            >100  Bα = 27.0                            41     BOCD-Phe               6.5  Aβ,Bα = 29.9 each               42     NAcetyl-L-Trp         120   Bα = 29.2                            43     NAcetyl-L-Trp Et ester                                                                              120   Aβ = 30.9                             44                                                                                    ##STR16##            120   Bα = 32.6                            45                                                                                    ##STR17##            >100  Bα = 28.7                            46     Nalpha-Acetyl-L-Orn   >120  Bα = 26.3                            47     L-Phenylalaninol      >120  Aα = 25.5                            48     L-Carnosine            80   Aα = 36.8                            49     L-(-)-Sparteine        1    Bα = 28.8                            50     NBenzyl-im-Benzyl-L-His                                                                              0.5  Bβ = 33.0                             51     NZHisp-NO.sub.2L-PheL-PheOMe                                                                         6.5  Aα = 38.4                            52     cyc(L-TyrL-His)       >6 <24                                                                              Bβ = 32.7                             53     NZL-His                30   Aα = 32.4                            54     Brucine                0.25 Bα = 32.4                            55     Nicotine               1    Aβ = 28.8                             56     cyc(NAcL-PheNAcGly)    74   Bα,Bβ = 25.8 each               57     cyc(L-ValL-His)        80   Aα = 38.1                            58     cyc(L-PheGly)         5 days                                                                              Bα = 26.8                            59     cyc(L-PheL-His)       <22   Bβ = 38.1                             60     L-Benzyl Hydantoin    >50 <74                                                                             Aβ = 26.9                             61     alpha-NMeL-His         24   Bβ = 31.0                             62     alpha-NBenzyl-L-His    6.5  Aα,Bβ =  30.6 each              63     ZL-HisL-Leu.H.sub.2 O >8 <22                                                                              Bα = 36.6                            64     NZL-HisGly            >100  Aα = 37.4                            65     GlyL-His.HCl          100   Aα = 27.3                            66     L-beta-Aspartyl-L-His 100   Bβ = 31.3                             67     ZL-HisL-Phe           >8 <22                                                                              Aα = 30.0                            68     BOCL-PheL-HisOMe      >22 <72                                                                             Aα = 27.6                            69     AOCL-PheL-HisOMe      >8 <22                                                                              Aα = 29.5                            70     BOCD-PhGlyD-HisOMe     4    Bβ = 34.2                             71     t-BOCN.sup.imbenzyl-L-His                                                                            1    Bβ = 31.0                             72     t-BOCN.sup.im im-tosyl-L-His                                                                        >54 <72                                                                             Bβ = 27.0                             73                                                                                    ##STR18##             46   Bβ = 28.4                             74     L-Histidinol.2HCl      28   Aα = 30.5                            75     L-beta-Imidazole Lactic acid                                                                        22-100                                                                              Bβ = 32.2                             76     NZL-Trp               >100  Bα = 28.5                            77     NZL-Trpp-NO.sub.2 Ph ester                                                                          >100  Aβ = 31.8                             78     ZD-PheD-TrpOMe        >100  Bα = 28.5                            79     alpha-NBenzoyl-L-Arginine                                                                           >100  Bα = 28.8                            80     Nalpha-Benzoyl-L-Argininamide.-                                                                     >100  Bα = 28.2                                   HCl.H.sub.2 O                                                          81     Nalpha-Acetyl-L-Lysine                                                                              >100  Bα = 29.2                            82     Nalpha-Acetyl-L-Lysine-OMe.HCl                                                                      100   Aβ = 28.2                             83     Cyc(L-ValGly)         100   Bα = 28.6                            84     3-MeHisOMe.2HCl       >8 <22                                                                              Aα = 31.2                            85     Cyc(GlyL-His)         30    Bβ = 32.9                             86     Poly-L-Histidine      <46   Aβ = 31.4                             87     ZL-HisL-PheL-Phe.OEt   6.5  Bβ = 32.9                             88     Nalpha-Benzoyl-L-HisOMe.HCl                                                                         >10 <22                                                                             Aα = 31.5                            89     t-BOCL-His            >30 <46                                                                             Aα = 30.8                            90     L-pGluL-HisGlyNH.sub.2                                                                               9    Bβ =  35.6                            91     L-pGluL-HisGlyHOAc     0.5  Aβ = 30.2                             92     L-beta-AlaL-3-MeHis.HNO.sub.3                                                                        6    Aα = 35.3                            93     N3,5-DNPyrL-His       >6 <54                                                                              Aα = 28.8                            94                                                                                    ##STR19##             3.5  Bβ = 26.9                             95                                                                                    ##STR20##             4.5  Aβ = 29.2                             96     NBenzoyl-L-His        <46   Aα = 30.3                            97     Nε-Acetyl-L-Lysine                                                                          >72   Aβ = 31.4                             98     alpha-NBenzoyl-L-Arg.OEt.HCl                                                                        >46 <54                                                                             Aβ = 26.9                             99                                                                                    ##STR21##             3.5  Bα = 26.5                            100    L-p-GluL-HisL-Pro.NH.sub.2                                                                           6    Bβ = 35.3                             101    Cyc(L-+-PheglyL-His)   24   Aα = 32.4                            102    Cyc(1-MeL-HisL-Phe)   10 min                                                                              Bβ = 41.3                             103    Cyc(2-naphthylala-L-His)                                                                            >6 <24                                                                              Bβ = 34.6                             104    ZL-Phegly-L-HisOMe     7    Aα = 32.8                            105    ZL-HomopheL-HisOMe    <23   Bβ = 30.6                             106                                                                                   ##STR22##            >7, <22                                                                             Aα = 38.9                            107    Angiotensin II Pentapeptide                                                                         48    Aα = 34.4                                   (TyrIleHisProPhe)                                                      108    ZRenin Substrate      >24, <48                                                                            Aα = 42.1                                   (ZProPheHisLeu                                                                ValTyr Serbeta-naphthylamide)                                          109    Glucagon-Hexapeptide  >24, <48                                                                            Aα = 31.1                                   (L-HisL-SerL-GluGlyL-ThrL-                                                    Phe)                                                                   __________________________________________________________________________

What is claimed is:
 1. A process for the preparation of anoptically-active cyanomethyl ester of an alpha-chiral carboxylic acid ora mixture enriched therein which comprises treating a non-symmetricalketene with a racemic or an optically-active alpha-hydroxynitrile orwith an aldehyde or ketone and cyanide ions in the presence of anoptically-active tertiary amine catalyst.
 2. A process according toclaim 1 wherein the optically-active amine is an optionally-substitutedalkyl, cycloalkyl, aromatic or heterocyclic di- or polyamine containingup to 40 carbon atoms or a polymer or copolymer thereof.
 3. A processaccording to claim 2 wherein the optically-active amine is anitrogen-base substituted amino acid, a di- or polypeptide thereof orthe reaction product of about one mole or three moles of a ketene withone mole of the nitrogen-base substituted amino acid or di- orpolypeptide thereof.
 4. A process according to claim 3 wherein the acidis an acyclic, carbocyclic, aromatic or heterocyclic amino acidcontaining up to 20 carbon atoms.
 5. A process according to claim 3wherein the nitrogen-base substituent is a moderate to weakly basicgroup.
 6. A process according to claim 5 wherein the nitrogen-basesubstituent is an optionally-substituted nitrogen-heterocyclic group oran optionally-substituted amino group.
 7. A process according to claim 1wherein the optically-active amine is a polymer or copolymer.
 8. Aprocess according to claim 1 wherein the optically-active amine is aheterocyclic amine or polymer of a heterocyclic amine.
 9. A processaccording to claim 8 wherein the amine is di- or polyaziridine, polymersof acryloylcinchonine alone or with N,N-diacrylolhexamethylenediamine,di- or poly(iminoisobutylethylene), polymers ofN-benzyl-2-pyrrolidinylmethyl ester with acrylic or a lower alkanoicacid.
 10. A process for the preparation of an optically-activecyanomethyl ester having an optically-active acid moiety or a mixtureenriched therein which comprises treating a non-symmetrical ketene witha racemic or an optically-active alpha-hydroxynitrile or with analdehyde or ketone and cyanide ions in the presence of anoptically-active histidine-containing catalyst.
 11. A process accordingto claim 10 wherein the non-symmetrical ketene is treated with analpha-hydroxynitrile having the S-configuration.
 12. A process accordingto claim 10 which is conducted in the presence of a non-hydroxylicsolvent.
 13. A process according to claim 12 wherein the solvent is ahydrocarbon, chlorinated hydrocarbon or ether.
 14. A process accordingto claim 10 wherein the catalyst is histidine or a histidine-containingdi- or polypeptide in which at least one of the histidyl-free N--H andfree COOH groups is optionally modified with a protecting group into theform of an amide, or an acid addition salt thereof, and ester grouprespectively; or the reaction product of one mole of a histidine orhistidine-containing di- or polypeptide with from about one mole of aketene.
 15. A process according to claim 14 wherein the di- orpolypeptide is linear or cyclic.
 16. A process according to claim 15wherein the peptide contains from about 2 to about 16 peptide units. 17.A process according to claim 16 wherein the catalyst is a dipeptide. 18.A process according to claim 14 wherein the di- or polypeptide alsocontains an alanine.
 19. A process according to claim 14 wherein theasymmetric carbon atoms in the histidine are in the D opticalconfiguration.
 20. A process according to claim 10 wherein the histidinemoiety in the catalyst is histidine, 3-methyl-histidine,1-methylhistidine, 1-ethyl-histidine, 1-propyl-histidine or1-benzyl-histidine.
 21. A process according to claim 18 wherein thealanine-containing moiety is alanine, beta-phenylalanine or3,4-dihydroxyphenylalanine.
 22. A process according to claim 3 whereinthe amino acid catalyst contains as a protecting group an organic acidor an alcohol.
 23. A process according to claim 22 wherein theprotecting group is an amino acid.
 24. A process according to claim 23wherein the protecting group is alanine, phenylalanine, glutamic acid orglycine.
 25. A process according to claim 18 wherein the catalyst is acyclic dipeptide containing a histidine moiety and an alanine moiety.26. A process according to claim 10 wherein the catalyst is opticallyactive and selected from histidine, alpha-methyl-histidine,1-methyl-histidine, cyclo(histidyl-histidine),(benzyloxycarbonylalanyl)histidine methyl ester,cyclo(alanyl-histidine), cyclo(beta-phenylalanyl-histidine),cyclo(beta-phenylalanyl-1-methylhistidine),cyclo(beta-phenylalanyl-3-methylhistidine), histidine methyl esterhydrochloride, histidine ethyl ester dihydrochloride, anserine,cyclo(valylhistidine), glycyl-histidine,cyclo(phenylalanyl-glycyl-histidine), cyclo(leucyl-histidine),cyclo(homophenylalanyl-histidine), cyclo(phenylalanyl-methylhistidine),N-alpha-(beta-naphthoyl)histidine, histidyl-alanine,histidyl-phenylalaninamide hydrochloride, histidylbeta-phenylalanine,cyclo(histidyl-proline) or cyclo(glycyl-histidine) in free or protectedform, or a reaction product thereof with a ketene.
 27. A processaccording to claim 10 wherein the catalyst is present in an amount ofabout 0.01 to about 5 mole percent based upon the weight of thealpha-hydroxynitrile, aldehyde or ketone.
 28. A process according toclaim 25 wherein the catalyst is present in an amount of about 2 molepercent based upon the weight of the alpha-hydroxynitrile, aldehyde orketone.
 29. A process according to claim 10 wherein the non-symmetricalketene is treated with an aldehyde or ketone and a source of hydrogencyanide.
 30. A process according to claim 29 wherein an aldehyde is usedwhich has the formula ##STR23## wherein Y is O; A, D and E eachindependently is a hydrogen atom having an atomic number of from 9 to35, inclusive, or an alkyl, alkenyl or alkoxy group containing 1 to 6carbon atoms, each optionally substituted by one or more halogen atomshaving an atomic number of from 9 to 35, inclusive.
 31. A processaccording to claim 31 wherein the aldehyde is 3-phenoxybenzaldehyde. 32.A process according to claim 1 wherein the alpha-hydroxynitrile is anS-alpha-cyano alcohol has the formula ##STR24## wherein Y is O; A, D,and E each independently is a hydrogen atom, a halogen atom having anatomic number of from 9 to 35, inclusive, or an alkyl or alkoxy groupcontaining 1 to 6 carbon atoms, each optionally substituted by one ormore halogen atoms having an atomic number of from 9 to 35, inclusive.33. A process according to claim 32 wherein A, D and E eachindependently is a hydrogen atom, a fluorine atom, a chlorine atom amethyl group, a trifluoromethyl group or a methoxy group.
 34. A processaccording to claim 33 wherein D is a hydrogen atom and A and E are ahydrogen atom or a fluorine atom and when either A or E is fluorine,each is located at the 4-position of the ring relative to the benzylcarbon when A or relative to the Y=O bearing carbon atom when E.
 35. Aprocess according to claim 34 wherein A is a fluorine atom at the4-position or a hydrogen atom and E is a hydrogen atom.
 36. A processaccording to claim 34 wherein the alpha-hydroxynitrile isS-alpha-cyano-3-phenoxybenzyl alcohol.
 37. A process according to claim34 wherein the alpha-hydroxynitrile isS-alpha-cyano-4-fluoro-3-phenoxybenzyl alcohol orS-alpha-cyano-3-(4-fluorophenoxy)benzyl alcohol.
 38. A process accordingto claim 11 wherein the optically-active ester isS-alpha-cyano-3-phenoxybenzyl S-alpha-isopropyl-4-chlorophenylacetate.39. A process according to claim 1 wherein the non-symmetrical ketenehas the formula ##STR25## wherein R¹ is isopropyl or cyclopropyloptionally substituted by one or more chlorine atoms; R² is an alkylgroup containing 1 to 6 carbon atoms; an alkenyl group containing 2 to 6carbon atoms; a naphthyl group, a phenyl group or a(benzyloxycarbonyl)phenylamino group each optionally ring substituted byone or more of halogen, alkyl, haloalkyl, alkoxy or haloalkoxy in whichthe halogens are bromine, chlorine or fluorine and the alkyl orcycloalkyl group contains 1 or 4 carbon atoms.
 40. A process accordingto claim 39 wherein in the non-symmetrical ketene R¹ is isopropyl; R² isa phenyl group para-substituted by halogen, alkyl or haloalkoxy in whichthe halogen is chlorine or fluorine and the alkyl contain 1 to 4 carbonatoms.
 41. A process according to claim 39 wherein the non-symmetricalketene is (4-chlorophenyl)isopropylketene,(4-(difluoromethoxy)phenyl)isopropylketene,(4-(trifluoromethyl)-3-(chlorophenyl)benzyloxycarbonylamino)isopropylketene.42. A process according to claim 1 wherein the ketene is prepared bytreating an acid halide with a tertiary amine.
 43. A process accordingto claim 42 wherein the acid halide is selected fromalpha-isopropyl(4-chlorophenyl)acetyl chloride,isopropyl((4-trifluoromethyl-3-chlorophenyl)(benzyloxycarbonyl)amino)acetylchloride or isopropyl(4-(difluoromethoxy)phenyl)acetyl chloride.
 44. Aprocess according to claim 43 wherein the acid halide isisopropyl(4-chlorophenyl)acetyl chloride.
 45. A process according toclaim 42 wherein the amine is a trialkylamine in which each alkyl groupcontains 1 to 4 carbon atoms.
 46. A process according to claim 45wherein the amine is triethylamine or trimethylamine.
 47. A processaccording to claim 46 wherein the reaction is conducted in the presenceof a solvent.
 48. A process according to claim 47 wherein the solvent isa non-hydroxylic solvent.
 49. A process according to claim 48 whereinthe solvent is a hydrocarbon, chlorinated hydrocarbon or ether.
 50. Aprocess according to claim 1 wherein the optically-activealpha-hydroxynitrile is prepared by treating the corresponding aldehydeor ketone with a source of cyanide ions in a solvent and in the presenceof a cyclo(D-phenylalanyl-D-histidine)dipeptide catalyst.
 51. A processaccording to claim 10 wherein the non-symmetrical ketene has the formula##STR26## wherein R¹ is isopropyl or cyclopropyl optionally substitutedby one or more chlorine atoms; R² is an alkyl group containing 1 to 6carbon atoms; an alkenyl group containing 2 to 6 carbon atoms; anaphthyl group, a phenyl group or a (benzyloxycarbonyl)phenylamino groupeach optionally ring substituted by one or more of halogen, alkyl,haloalkyl, alkoxy or haloalkoxy in which the halogens are bromine,chlorine or fluorine and the alkyl or cycloalkyl group contains 1 or 4carbon atoms; an alpha-hydroxynitrile is used of the formula ##STR27##wherein Y is O; A, D, and E each independently is a hydrogen atom, ahalogen atom having an atomic number of from 9 to 35, inclusive, or analkyl or alkoxy group containing 1 to 6 carbon atoms, each optionallysubstituted by one or more halogen atoms having an atomic number of from9 to 35, inclusive, and the catalyst is histidine or ahistidine-containing di- or polypeptide in which at least one of thehistidyl-free N--H and free COOH groups is optionally modified with aprotecting group into the form of an amide, or an acid addition saltthereof, and ester group respectively; or the reaction product of onemole of a histidine or histidine-containing di- or polypeptide with fromabout one mole of a ketene.
 52. A process according to claim 51 whereinin the non-symmetrical ketene R¹ is isopropyl, R² is a phenyl grouppara-substituted by halogen, alkyl or haloalkoxy in which the halogen ischlorine or fluorine and the alkyl contains 1 to 4 carbon atoms; in thealpha-hydroxynitrile A, D and E each independently is a hydrogen atom, afluorine atom, a chlorine atom, a methyl group, a trifluoromethyl groupor a methoxy group; and the catalyst is a di- or polypeptide alsocontaining an alanine moiety.
 53. A process according to claim 52wherein the non-symmetrical ketene is (4-chlorophenyl)isopropylketene,the alpha-hydroxynitrile is S-alpha-cyano-3-phenoxybenzyl alcohol andthe catalyst is a cyclo(D-phenylalanyl-D-histidine).